Stent range transducers and methods of use

ABSTRACT

The present invention provides exemplary apparatus, systems and methods for accurately delivering and positioning a stent within a body lumen, particularly within a bifurcated body lumen. In one embodiment, a stent delivery system ( 100 ) includes a catheter ( 15 ) comprising a catheter body having a distal end, a proximal end, a longitudinal axis ( 200 ) and a lumen. An expansion device, which in one embodiment is a balloon ( 20 ), is disposed near the catheter body distal end, and a stent ( 10 ) having a side hole ( 12 ) is disposed over the expansion device. An ultrasound transducer ( 22 ) is disposed near the catheter body distal end and positioned for transmitting and receiving ultrasound signals through the side hole to help properly align the stent side hole with a branch vessel ( 16 ).

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/155,611 filed on Sep. 23, 1999, the completedisclosure of which is incorporated herein by reference.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0002] This application is being filed concurrently with related U.S.patent app. Ser. No. ______ (Attorney Docket Number 019601-000410),entitled “Differentially Expanding Stent and Methods of Use”; and U.S.patent app. Ser. No. ______ (Attorney Docket Number 019601-000430),entitled, “Bifurcation Stent Systems and Methods,” the completedisclosures of which are incorporated herein by reference and filed at adate even herewith.

BACKGROUND OF THE INVENTION

[0003] A type of endoprosthesis device, commonly referred to as a stent,may be placed or implanted within a vein, artery or other hollow bodyorgan or lumen for treating occlusions, stenoses, or aneurysms of avessel by reinforcing the wall of the vessel or by expanding the vessel.Stents have been used to treat dissections in blood vessel walls causedby balloon angioplasty of the coronary arteries as well as peripheralarteries and to improve angioplasty results by preventing elastic recoiland remodeling of the vessel wall. Two randomized multicenter trialshave recently shown a lower restenosis rate in stent treated coronaryarteries compared with balloon angioplasty alone (Serruys, P W et al.,New England Journal of Medicine 331: 489-495 (1994) and Fischman, D L etal. New England Journal of Medicine 331:496-501 (1994)). Stents havebeen successfully implanted in the urinary tract, the bile duct, theesophagus and the tracheo-bronchial tree to reinforce those body organs,as well as implanted into the neurovascular, peripheral vascular,coronary, cardiac, and renal systems, among others. The term “stent” asused in this Application is a device which is intraluminally implantedwithin bodily vessels to reinforce collapsing, dissected, partiallyoccluded, weakened, diseased or abnormally dilated or small segments ofa vessel wall.

[0004] One of the drawbacks of conventional stents is that they aredifficult to position. In general, positioning a stent involves movingthe stent to the desired position and then maintaining the positionwhile the stent is deployed. Accurate positioning is critical to properoperation of the stent. For example, the use of such stents to treatdiseased vessels at or near a bifurcation (branch point) of a vesselrequires very accurate positioning otherwise, there is a potential forcompromising the degree of patency of the main vessel and/or itsbranches, or the bifurcation point. Compromising the bifurcation pointlimits the ability to insert a branch stent into the side branch if theresult of treatment of the main vessel is suboptimal. Suboptimal resultsmay occur as a result of several mechanisms, such as displacing diseasedtissue, plaque shifting, vessel spasm, dissection with or withoutintimal flaps, thrombosis, and embolism.

[0005] In light of the foregoing, it would be desirable to providemethods, apparatus and/or systems to increase stent positioningaccuracy, particularly when used with bifurcated body lumens.

SUMMARY OF THE INVENTION

[0006] The present invention provides exemplary apparatus, systems andmethods for accurately delivering and positioning a stent within a bodylumen, particularly within a bifurcated body lumen. In one embodiment, astent delivery system according to the present invention includes acatheter comprising a catheter body having a distal end, a proximal end,a longitudinal axis and a lumen. An expansion device, which in oneembodiment is a balloon, is disposed near the catheter body distal end,and a stent having a side hole is disposed over the expansion device. Anultrasound transducer is disposed near the catheter body distal end andpositioned for transmitting and receiving ultrasound signals through theside hole. In this manner, an intravascular ultrasound catheter andsystem is used to help properly position the stent, and properly alignthe stent side hole with a branch vessel.

[0007] The ultrasound transducer is disposed inside the expansiondevice, or between the expansion device and stent in alternativeembodiments. Preferably, the ultrasound transducer is adapted to beaxially translated along the longitudinal axis and/or rotated relativeto the longitudinal axis. In this manner, the ultrasound transducer maybe used to image surrounding fluids and tissue to assure proper stentalignment.

[0008] In some embodiments, the stent delivery system further includes atransducer housing to which the transducer is coupled. The housing hasdistal and proximal ends, with a passageway passing therethrough. Thepassageway has a guidewire partially disposed therein in one embodiment.The housing proximal end is coupled to a drive cable, which in oneembodiment is adapted to rotate the housing relative to the catheterdistal end. A controller may be included, coupled to the transducer, tofacilitate system operation.

[0009] The present invention further provides methods of positioning astent having a side opening. In one embodiment, the method includesproviding a stent delivery system ostensibly as described herein,positioning the stent delivery system in a body lumen, imaging the bodylumen with the transducer to locate an ostium of a branch vessel, andaligning the stent side hole with the ostium. In this manner, the use ofultrasound imaging facilitates proper stent side hole alignment with thebranch vessel.

[0010] In one embodiment, the ultrasound transducer is adapted to rotaterelative to the longitudinal axis. The imaging further includes rotatingthe transducer to image a cross section of the body lumen. Similarly, inone embodiment, aligning the stent side hole includes axiallytranslating the stent along the longitudinal axis and/or rotating thestent about the longitudinal axis. In some embodiments, a body lumenguidewire is introduced, and the catheter is advanced over the guidewireto be near the branch vessel.

[0011] In one embodiment, the stent delivery system is conveniently partof a kit, which includes instructions for use setting forth a method forpositioning the stent in a bifurcated body lumen so that the side holeis substantially aligned with an ostium of a branch vessel.

[0012] Other objects, features and advantages of the present inventionwill become more fully apparent from the following detailed description,the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 depicts an overall view of a stent according to the presentinvention disposed in a body lumen;

[0014]FIG. 2 depicts an overall view of a stent delivery apparatusaccording to the present invention;

[0015]FIGS. 3A and 3B provide side and front cross-sectional views,respectively, of the apparatus shown in FIG. 2;

[0016]FIGS. 4A and 4B depict an overall view and a side cross-sectionalview, respectively, of an ultrasound imaging device according to thepresent invention;

[0017]FIGS. 5A and 5B depict simplified views of a stent delivery systemaccording to the present invention disposed in a body lumen;

[0018]FIGS. 5C and 5D plot transmitted and received ultrasound energysignals as a function of time for stent delivery systems positionedaccording to FIGS. 5A and 5B, respectively;

[0019]FIGS. 6A and 6B depict ultrasound images of a stent within a bodylumen;

[0020] FIGS. 7A-7C depict simplified cross-sectional images of a vesselhaving a stent delivery system according to the present inventiondisposed therein;

[0021] FIGS. 8A-8C depict simplified views of a stent delivery systemdisposed in a body lumen in positions which correspond to the imagesshown in FIGS. 7A-7C;

[0022]FIG. 9 depicts a simplified schematic of a stent delivery systemaccording to the present invention;

[0023]FIG. 10 depicts a simplified schematic of imaging catheterelectronics for use with the present invention; and

[0024]FIG. 11 depicts a kit including apparatus and instructions for useaccording to the present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0025]FIG. 1 depicts a simplified view showing a stent 10 disposedwithin a main vessel 14. Main vessel 14 may comprise an artery, a veinor a wide range of body lumens into which it is desirable to disposestent 10. Stent 10 includes a side hole 12, which is in registry with anostium of a branch vessel 16. In many cases, it is desirable to haveside hole 12 aligned with the ostium of branch vessel 16 to, forexample, permit the introduction of a branch stent or second stent (notshown) into branch vessel 16. The alignment of side hole 12 with branchvessel 16 is often crucial to the proper use of stent 10, and prior artmethods for alignment are replete with problems. Apparatus, systems andmethods of the present invention are directed, in part, to properlyaligning side hole 12 with branch vessel 16 by using an imagingtransducer or catheter with stent 10.

[0026] Turning now to FIGS. 2, 3A, 3B, 4A and 4B, an exemplary stentdelivery system 15 according to the present invention will be described.Stent 10 is shown in a non-expanded state, crimped around a balloon 20.Balloon 20 provides a mechanism for expanding stent 10 when stent 10 isplaced at a desired location within a body lumen. It will be appreciatedby those skilled in the art that other methods of expanding stent 10fall within the scope of the present invention. System 15 furtherincludes a transducer 22 to provide an imaging capability to helpproperly position side hole 12. Transducer 22 typically comprisespiezoelectric materials for the conversion of electrical signals intomechanical energy, more specifically, sound energy. As best shown inFIG. 3A, transducer 22 is coupled to a housing 24. In one embodiment,housing 24 is disposed within balloon 20, as shown in FIG. 3A.Transducer housing 24 is positioned so that ultrasound signalstransmitted from transducer 22 pass through side hole 12 into thesurrounding fluid or tissue. In this manner, and as further describedbelow, transducer 22 may be used to indicate when side hole 12 isproperly aligned with a branch vessel 16 as opposed to facing a wall ofmain vessel 14. In an alternative embodiment (not shown), transducer 22is mounted on an outer surface of balloon 25 or positioned betweenballoon 25 and stent 10. For example, transducer 22 may be mounted onballoon 25 within sidehole 12. In one embodiment, a guidewire 18 isdisposed through balloon 20, and is used to help guide the stentdelivery system to a desired region within a body lumen.

[0027] Turning now to FIG. 3B, a cross-sectional view taken along line3B-3B is shown. Stent 10 comprises a plurality of struts 26 configuredin a desired relationship. It will be appreciated by those skilled inthe art that the precise configuration of stent struts 26 may varywidely within the scope of the present invention. Further, the presentinvention may use stent configurations disclosed in U.S. applicationSer. No. ______ (Attorney Docket No. 19601-000410), and U.S. applicationSer. No. ______ (Attorney Docket No. 19601-000430), the completedisclosures of which have been previously incorporated by reference.Stent 10, including struts 26, are crimped around balloon 20. Theimaging catheter, which includes transducer 22, is disposed within aballoon lumen 30 inside balloon 25. The imaging apparatus has an outermember 32 and an inner member 34 defining a wire lumen 38 therebetween.A passageway 40 is formed within inner member 34. Wire lumen 38 is usedto maintain transducer wires 36, which typically connect opposing facesof transducer 22 with a controller (not shown). Passageway 40, in oneembodiment, defines a guidewire lumen 40 through which guidewire 18extends. In this manner, guidewire 18 extends through housing 24 tofacilitate proper alignment between transducer 22 and stent 10.

[0028] Transducer housing 24 is adapted to be translated axially along alongitudinal axis 200. In one embodiment, the axial translation oftransducer housing 24 is made relative to stent 10. Alternatively,balloon 20 and transducer housing 24 are disposed such that they move inparallel, maintaining the proper configuration of transducer 22 withrespect to side hole 12.

[0029]FIGS. 4A and 4B depict additional details of transducer 22 andhousing 24. In one embodiment, a drive cable 44 is coupled to a proximalend of housing 24. FIG. 4A further depicts passageway 40 which extendsthrough housing 24. In one embodiment, drive cable 44 comprises twocounterwound cables made of stainless steel, nitinol or the like. Such adrive cable facilitates its introduction into tortuous vasculatures.Drive cable 44 further permits rotation of housing 24, and hence therotation of transducer 22. Preferably, such rotation is made relative tolongitudinal axis 18.

[0030]FIG. 4B is a side cross-sectional view of a portion of the imagingcatheter. As shown, an optional sheath 46 may be used to enclose drivecable 44. Sheath 46 operates to protect balloon 20 during rotation ofdrive cable 44. Further, sheath 46 provides a substantially smooth outersurface for embodiments in which the imaging apparatus is translatedaxially relative to balloon 20 and/or stent 10. Sheath 46 may comprisepolyethylene, as well as a wide range of other materials. In oneembodiment, sheath 46, drive cable 44 and an inner sleeve 48 correspondto outer member 32 depicted in FIG. 3B.

[0031] Drive cable 44 defines guidewire lumen 38 into which transducerwires 36 are disposed. Inner member 34 maintains transducer wires 36within wire lumen 38. Further, inner member 34 defines passageway 40through which guidewire 18 may be disposed. In an alternativeembodiment, guidewire 18 passes through balloon lumen 30, adjacent todrive cable 44 or sheath 46.

[0032]FIGS. 5A and 5B depict a simplified view of the imaging of a bodylumen with transducer 22. Similarly, FIGS. 5C and 5D depict theintensity of transmitted and reflected signals when transducer 22 isactivated at the positions shown in FIGS. 5A and 5B, respectively. Forexample, in FIG. 5A, a voltage is applied across transducer 22 togenerate ultrasound signals 16 which are transmitted from transducer 22to surrounding fluids and tissue. When signals 16 encounter a change inmedium, and more specifically a change in the density of the materialthrough which the signals are passing, at least a portion of signal 16is reflected back toward transducer 22. Transducer 22 receives thereflected signal and transmits a corresponding voltage through wires 36to a controller (not shown) for processing. When transducer 22 ispositioned as shown in FIG. 5A, signals 16 travel down a portion of thebranch vessels 16 before being reflected by a vessel wall, occlusion, orthe like. Hence, as can be seen in FIG. 5C, the reflected signal isreceived after some time delay relative to the initial signal pulse.Additionally, the travel time for the reflected signal results in muchof the sound energy being lost in blood or other fluid. Hence acomparatively weak signal is returned to transducer 22. Correspondingly,if transducer 22 is disposed adjacent a wall 80, such as shown in FIG.5B, the reflected signal is received much sooner and occurs at a greaterintensity than the alignment shown in FIG. 5A. The stronger echo orreturn signal is depicted in FIG. 5D. In this manner, ultrasoundimaging, including the calculated time delay between the original pulseand the reflected signal, can be used to determine whether transducer 22is in alignment with branch vessel 16.

[0033] Turning now to FIGS. 6A and 6B, cross-sectional ultrasound imagesof a stent disposed in a body lumen are shown. FIG. 6A depicts atwo-dimensional image showing stent struts 26 disposed about a centercatheter or transducer 22. The imaging performed by transducer 22reveals blood speckles 68, guidewire 18 and a guidewire shadow 64, aswell as a plaque 66 or other vessel wall imperfections. FIG. 6A depictsa generally uniform strut 26 structure and may exemplify thecross-sectional view of a stent that does not have a side hole, or thecross-sectional view of stent 10 when transducer 22 is not aligned withside hole 12. For example, transducer 22 may be located proximal ordistal to side hole 12. FIG. 6B depicts a similar view as shown in 6A,except the imaging transducer 22 is aligned with side hole 12. As aresult, a gap 62 is seen in the strut 26 pattern. It is the imaging ofgap 62 which helps align side hole 12 with branch vessel 16 according toone embodiment of the present invention.

[0034] Images depicted in FIGS. 6A and 6B may be created in several waysaccording to the present invention. In one embodiment as previouslydescribed, transducer 22 is rotated about the longitudinal axis 200 bydrive cable 44. In this manner, a single transducer 22 can produce a twodimensional, 360 degree image plane as shown in FIGS. 6A and 6B. In analternative embodiment, a ring of transducer elements (not shown) aredisposed in the catheter distal end to produce a two dimensional, 360degree image plane without the need to rotate the ring of elements,although the elements may be rotated in another embodiment. The fixedring of transducer elements may be disposed on an outer surface ofballoon 25, between balloon 25 and stent 10. Preferably, such anembodiment has at least some of the transducer elements disposed onballoon 25 where sidehole 12 overlies. In this manner, some of thetransducer elements will produce gap 62 as shown in FIG. 6B. In analternative embodiment, the ring of transducer elements are disposed onthe outer surface of a sheath, similar to outer member 32 shown in FIG.3B. In this embodiment, the ring of transducer elements are disposedinside balloon lumen 30. In still another embodiment, the ring oftransducer elements are not used to produce an image as in FIGS. 6A and6B, but instead are used to indicate side hole to branch vesselalignment in accordance with the discussion accompanying FIG. 10.

[0035]FIG. 7, in conjunction with FIG. 8, are helpful in explainingmethods of the present invention. FIGS. 7A-7C depict simplifiedultrasound cross-sectional images of a stent delivery apparatus disposedwithin a body lumen, such as main vessel 14. The images shown in FIGS.7A-7C correspond to the stent and ultrasound transducer 22 positionsshown in FIGS. 8A-8C. For example, FIGS. 7A and 8A depict stent 10disposed within main vessel 14 where stent 10 is not adjacent to oraligned with branch vessel 16. Hence, the image of FIG. 7A shows agenerally uniform main vessel wall 80 not adjacent to the bifurcation.As a result, gap 62 corresponding to side hole 12 is not aligned withbranch vessel 16. In such a configuration, it is desirable to axiallytranslate transducer 22 and stent 10 to continue to search for thedesired branch vessel 16.

[0036]FIGS. 7B and 8B depict stent 10 in axial or longitudinal alignmentwith branch vessel 16, however, side hole 12 is facing away from theostium of branch vessel 16. The image shown in FIG. 7B has an extendedregion 70 corresponding to the delayed signal return associated with thesignals traveling at least partially down branch vessel 16. In otherwords, the branch vessel 16 opening is now in view of transducer 22.However, as shown in FIG. 7B, gap 62 is still depicted facing mainvessel wall 80. In such a configuration, it is then desirable to rotatestent 10 to properly align side hole 12 with the ostium of branch vessel16. The desired configuration showing the alignment of side hole 12 withthe ostium of branch vessel 16 is shown in FIGS. 7C and 8C. FIG. 7C nowdepicts gap 62 in registry with extended region 70. Such an imagecorresponds with the alignment of side hole 12 with the ostium of branchvessel 16, as shown in FIG. 8C. In this manner, the use of ultrasoundimaging helps facilitate the alignment of side hole 12 with branchvessel 16. Preferably, ultrasound transducer 22 is aligned with sidehole 12 at all times, so ultrasound signals are transmitted to and fromtransducer 22 through side hole 12. In this manner, gap 62 will be seenon the ultrasound images. Alternatively, transducer 22 may move freelyrelative to stent 10. In such an embodiment, it may be desirable tofirst image with transducer 22 to locate side hole 12, with reference tothe images of FIGS. 6A and 6B as guidance.

[0037]FIG. 9 depicts an exemplary stent delivery system 100 according tothe present invention. Delivery system 100 includes a console 110 havinga controller 120 and a display 130. Controller 120 is coupled to a drivemotor 140, which in one embodiment is used to rotate an ultrasoundtransducer 180. Transducer 180 is similar to transducer 22 described inconjunction with earlier Figures. Further, transducer 180 may be anarray of transducers as previously described. As shown in FIG. 9, acatheter 150 is provided having a proximal end 152 and a distal end 154to which transducer 180 is coupled. Catheters for delivering stentsaccording to the present invention are described in further detail inU.S. application Ser. No. ______ (Attorney Docket No. 19601-000320),entitled “Catheter With Side Sheath And Methods,” and U.S. applicationSer. No. ______ (Attorney Docket No. 19601-000120), entitled “ExtendibleStent Apparatus”, the complete disclosures of which are incorporatedherein by reference.

[0038] As shown, system 100 includes a guidewire 190 over which aballoon 170 and a stent 160 are disposed. A control circuitry, as shownin FIG. 10, is used to transmit an electrical signal from a voltagesource to transducer 180 to generate imaging ultrasound signals as iswell known in the art. Transducer 180 is then used to position stent 160such that a side hole (not shown) of stent 160 is properly aligned withan ostium of a branch vessel.

[0039]FIG. 10 depicts a simplified schematic of one embodiment ofcontrol circuitry 300 for use with the present invention. A high voltagesource 310 is coupled to an RF pulse generator 320 which generates anelectrical pulse for transmission to transducer 330 by way of atransmit/receive switch 340. Transducer 330 receives the electricalsignal as voltage applied across opposing surfaces of transducer 330.The transducer material, preferably piezoelectric material, generates asoundwave which propagates from the surface of transducer 330. Aspreviously noted, the soundwaves reflect off changes in medium density,such as the wall of a vascular vessel, and a portion of the signalreturns to transducer 330. Transducer 330 then transmits the receivedsignal to transmit/receive switch 340 and a receiver filer 350. Timingcontrol and logic circuitry 360 coordinates RF pulse generator 320,transmit/receive switch 340 and receiver filter 350 operation.

[0040] As previously described, the time delay of signals received fromechoes off the branch vessel are greater than the time delay fromsignals received off of the main vessel walls. In one embodiment,receiver filter 350 may be used to indicate to a user of system 100 thatside hole 11 is aligned, or not aligned, with branch vessel 14. Forexample, one or more indicator lights 380 may be used to indicate sidehole alignment (green) or non-alignment (red). In some embodiments,circuitry 300 does not produce a visual image of the body lumen.Instead, the signals received from transducer 330 are used to indicatesidehole to branch vessel alignment. A power supply 370 facilitatesoperation of the individual electrical components.

[0041] As shown in FIG. 11, stent, catheter and/or system 410 may beconveniently included as part of a kit 400. Kit 400 includesinstructions for use 420 which set forth various procedures fordeploying stent 10 and imaging using transducer 22 using any of thetechniques previously described. Instructions for use 420 may be inwritten or in machine readable form. Further, it will be appreciatedthat kit 400 may alternatively include any of the other elementsdescribed herein, such as imaging catheter 15, balloon 20, and the like.Further, instructions 420 may describe use of any of the other elements.

[0042] The invention has now been described in detail for purposes ofclarity of understanding. However, it will be appreciated that certainchanges and modifications may be practiced within the scope of theappended claims. For example, while transducer 22 is generally describedas coupled to a drive cable 44 facilitating transducer rotation,transducer 22 also may be fixed relative to stent 10. In such anembodiment, transducer 22 would comprise a side-looking transducerfacing side hole 12. In this manner, transducer 22 would be aligned withside hole 12 to facilitate side hole 12 alignment with branch vessel 16.Such a configuration would produce images similar to that shown in FIG.6B, but comprising a pie-shaped portion of the image. Rotation oftransducer 22 could then occur by rotating stent 10, with transducer 22maintaining a vigilant eye towards side hole 12.

What is claimed is:
 1. A stent delivery system, comprising: a cathetercomprising a catheter body having a distal end, a proximal end, alongitudinal axis and a lumen; an expansion device disposed near thecatheter body distal end; a stent having a side hole, said stent beingdisposed over the expansion device; and an ultrasound transducerdisposed near the catheter body distal end and positioned fortransmitting and receiving ultrasound signals through said side hole. 2.The stent delivery system as in claim 1 wherein said expansion devicecomprises a balloon.
 3. The stent delivery system as in claim 1 whereinsaid ultrasound transducer is disposed inside said expansion device. 4.The stent delivery system as in claim 1 wherein said ultrasoundtransducer is disposed between said expansion device and said stent. 5.The stent delivery system as in claim 1 wherein said ultrasoundtransducer is adapted to be axially translated along said longitudinalaxis.
 6. The stent delivery system as in claim 1 wherein said ultrasoundtransducer is adapted to be rotated relative to said longitudinal axis.7. The stent delivery system as in claim 1 further comprising atransducer housing to which said transducer is coupled, said housinghaving a distal end, a proximal end that is coupled to a drive cable,and a passageway passing through said housing between said proximal anddistal ends.
 8. The stent delivery system as in claim 7 wherein saiddrive cable is adapted to rotate said housing relative to said catheterdistal end.
 9. The stent delivery system as in claim 1 furthercomprising a guidewire at least partially disposed in said lumen. 10.The stent delivery system as in claim 7 further comprising a guidewireat least partially disposed in said lumen and passing through saidpassageway.
 11. The stent delivery system as in claim 1 furthercomprising a controller coupled to said transducer.
 12. A stent deliverysystem, said system comprising: a catheter comprising a catheter bodyhaving a distal end, a proximal end and a lumen; a balloon disposed nearsaid catheter body distal end; a stent having a side hole, said stentdisposed over said balloon; an ultrasound transducer housing having adistal end, a proximal end, and a passage through said housing betweensaid distal and proximal ends, said housing having a transducer coupledthereto; and a positioning guidewire at least partially disposed in saidcatheter lumen, said guidewire passing through said transducer housingpassageway.
 13. A method of positioning a stent having a side opening,said method comprising: providing a stent delivery system, comprising; acatheter comprising a catheter body having a distal end, a proximal end,a longitudinal axis and a lumen; an expansion device disposed near thecatheter body distal end; a stent having a side hole, said stent beingdisposed over the expansion device; and an ultrasound transducerdisposed near the catheter body distal end for transmitting andreceiving ultrasound signals through said side hole; positioning saidstent delivery system in a body lumen; imaging said body lumen with saidtransducer to locate an ostium of a branch vessel; and aligning saidstent side hole with said ostium.
 14. The method of claim 13 whereinsaid transducer is disposed in said expansion device.
 15. The method ofclaim 13 wherein said ultrasound transducer is adapted to rotaterelative to said longitudinal axis, and said imaging further comprisesrotating said transducer to image a cross section of said body lumen.16. The method of claim 13 wherein said aligning comprises axiallytranslating said stent.
 17. The method of claim 13 wherein said aligningcomprises rotating said stent about said longitudinal axis.
 18. Themethod of claim 13 further comprising: introducing a body lumenguidewire into said body lumen; and advancing said catheter over theguidewire and through said body lumen to be near said branch vessel. 19.The method of claim 18 wherein said transducer is coupled to a housinghaving a passageway through which said guidewire passes, said advancingalso advancing said transducer housing to be near said branch vessel.20. The method of claim 13 wherein said stent delivery system furthercomprises a controller coupled to said transducer for controlling saidimaging.
 21. A kit comprising: a stent delivery system as in claim 1;and instructions for use setting forth a method for positioning saidstent in a bifurcated body lumen so that said side hole is substantiallyaligned with an ostium of a branch vessel.